The present invention relates generally to display backlighting systems, and in particular, to a display backlighting system for illuminating a liquid crystal display in a portable electronics device, such as a wireless telephone.
Liquid crystal displays (LCD) and other displays are used in many electronic devices, including portable electronic devices. In many electronic devices employing liquid crystal and other displays, the display is illuminated to facilitate better perception by a user. One common way of illuminating a display is to backlight the display. Typically, the goal of backlighting is to route light from a source efficiently and evenly into the planer area (backplane) of a light pipe directly behind the LCD so that it may escape forward through the LCD, giving the appearance of an illuminated display. Backlighting requires that light from the light source be emitted into an entrance lens of the light pipe and distributed evenly within the light pipe.
Various techniques known to those of skill in the art are used to evenly distribute the light within the light pipe. In a portable electronic device employing display backlighting, the light source is mounted to a printed circuit board (PCB), upon which other components implementing the function of the electronic device are also mounted. A typical light source for backlighting a display consists of one or more light emitting diodes (LEDs). Two types of LEDs, top firing LEDs and side firing LEDs are normally used. Top firing LEDs emit light generally perpendicular to the mounting surface of the printed circuit board, while side firing LEDs emit light in an area generally parallel to the mounting surface of the printed circuit board.
In portable electronic devices in which the size of the device is optimally small, the LCD is mounted with the readable surface of the display being approximately parallel to the PCB. In this arrangement, side firing LEDs generally offer increased optical efficiency due to their ability to emit light parallel to and directly into the light pipe backplane. However, the use of side firing LEDs requires positioning the backplane of the light pipe at the same level as the LED and very close to the surface of the PCB. This arrangement of the LED is problematic, in that having to place the backplane of the light pipe at a close proximity to the PCB corrupts the ability to place PCB mounted electrical components in the area on the PCB taken up by the flat light pipe.
Therefore a need exists for a display backlighting system that provides sufficient illumination for a display without consuming areas of the PCB that could otherwise be populated with critically needed electronic components.